1. Technical Field
The present invention relates to an information disk device and its reading method, and more particularly to a disk reproducing apparatus for simultaneous reading of data in plural tracks of an optical disk used in a CD-ROM or the like, and a method of reading the same.
2. Background Art
In an optical disk device such as CD-ROM device, recently, a high-speed reading function is required. As a method of realizing this, a multi-track disk reproducing apparatus for simultaneously reading data in plural adjacent tracks has been proposed. Hitherto, in the case of reading out data by a multi-track disk reproducing apparatus, a method disclosed in U.S. Pat. No. 5,627,805 has been known. This method is characterized that the data being read out from plural tracks are, after EFM demodulation, once stored in a buffer memory of a large capacity, and aligned in the sequence on the disk, and decoded according to CIRC sequentially from the head data. In the case of CD-ROM data, after CIRC decoding, further, ECC error correction is made on the buffer memory, and the output is sent into the host computer through interface means.
In the CIRC coding method of CD, in order to cope with a local disk defect, the data is recorded by a technique called interleaving, as being distributed in 108 CD frames at maximum. Accordingly, the data is stored in a buffer for frame data sequentially from the beginning, and corresponding bit data is extracted from the distributed-recorded data, and the corresponding data needs to be decoded by putting it into the decoding circuit. Therefore, in the method disclosed in U.S. Pat. No. 5,627,805, it is required to prepare a buffer memory for frame data of at least the amount of one rotation of diskxc3x97the number of tracks that can be read simultaneously. Further, in the case of CD, which is recorded at a constant linear speed, the data memory capacity per a rotation of disk is greater in the outer periphery of the disk than in the inner periphery. Therefore, it requires a buffer memory for frame data having of the maximum recording capacity per rotation.
However, since the data before CIRC decoding contains error correction information, the data redundancy is great, and a memory of a larger capacity is needed, and hence the cost is higher. Yet, until the data of one rotation is read out completely, decoding data in the second track and after cannot be started. After reading out the data of one rotation, when restarting reading by advancing the track, undecoded data is left over in the buffer memory for frame data. Therefore, reading cannot be not restarted until decoding the data is completed, or an extra buffer memory for frame data must be preserved. In the latter case, it is necessary to prepare a buffer memory for storing data of a large redundancy including the error correction information before CIRC decoding as mentioned above, and the efficiency is very poor.
To solve the problems, the invention presents a multi-track disk reproducing apparatus for reproducing simultaneously signals of adjacent plural tracks on an information disk having plural tracks formed spirally on a recording surface, and recording data coded by using an interleaving technique as well as adding error correction information. The appratus comprises signal reproducing means for reproducing signals of adjacent plural tracks simultaneously from an information disk, data converting means for converting output signals read from the plurality of tracks into digital data, memory means for storing the converted data read from the plurality of tracks longer than the interleaving length, decoding means for decoding and outputting desired data from the data stored in the memory means, data aligning means for aligning the data output in parallel in the sequence of addresses on the information disk, and data output mans for outputting the aligned valid data to the outside of the disk reproducing apparatus.
According to the invention, the buffer memory for storing before-decoding coded data by the interleaving technique of a larger redundancy requires only the capacity of minimum limit necessary for decoding. The data reduced in redundancy is aligned on the buffer memory, so that the buffer memory in the entire system can be further decreased in capacity. Moreover, decoding can be done in parallel by each track. Also, it is not necessary to wait for rotation of the disk until the desired data comes to the position of the reader at the time of advancing the track to be reproduced by making a track-jump after reading the data of one rotation, as well as at the time of restarting reading after moving the reader in the signal reproducing means from a remote track. Thus the data can be reproduced efficiently.